Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Golf balls are typically constructed with polymer compositions including, for example, polybutadiene rubber, polyurethanes, polyamides, ionomers, and blends thereof. Playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from modification(s) of golf ball materials and/or construction can be quite significant.
Ionomers, particularly ethylene-based ionomers, are a preferred group of polymers for golf ball layers because of their toughness, durability, and wide range of hardness values. Ionomers initially became popular golf ball cover materials due to their excellent impact resistance and their thermoplasticity, which permits the material to be economically applied via injection or compression molding techniques.
Golf ball manufacturers have blended high molecular weight acid-containing polymers and low molecular weight acid-containing polymers because each is known to have drawbacks when used in golf ball ionomer compositions. On the one hand, high molecular weight acid-containing polymers tend to produce compositions having excellent physical properties such as heat stability, yet suffer from low melt flow and attendant poor processability. On the other hand, low molecular weight acid-containing polymers generally result in compositions having excellent melt flow, yet poor physical properties such as heat stability. Blending of high and low molecular weight acid-containing polymers has been found to overcome these drawbacks and achieve an acceptable balance between good physical properties (such as heat stability) and melt flow (processability).
However, it would be more efficient and cost effective to develop improved ionomeric formulations that don't require blending high and low molecular weight acid-containing polymers—especially those which meanwhile retain original properties well. In this regard, it can be difficult for a material to retain its original properties long term when problems occur such as migration of ingredients within and between adjacent golf ball layers. This generally changes the material, which can alter important golf ball properties including durability, adhesion, resilience (CoR), compression, and soft feel.
There is therefore a need for such improved ionomeric layer formulations and golf balls containing same, which would be particularly useful if producible within existing golf ball manufacturing systems. Golf balls of the present invention and the methods of making same address and solve this need.